Basic GIS Operation / GIS Analysis

Fundamental of GIS & Remote Sensing (GLS280) Chapter 4

Basic GIS Operation /GIS Analysis

Lecture Outline At the end of this chapter, student should able to: -Understand GIS analysis -Differentiate different type f GIS analysis

GIS Analysis/Operation 

The scope of GIS analysis are varies among GIS disciplines.

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GIS users in hydrology will likely emphasize the importance of terrain analysis and hydrologic modeling.

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GIS users in wildlife management will more interested in analytical function dealing with wildlife point location.

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GIS companies take two general approaches in packaging their product.

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One prepares a set of basic tools used by most GIS users and others prepare extensions design for specific applications, such as hydrologic modeling.

GIS Analysis basic GIS tools In basic GIS tools, they are an analysis tools which was grouped into 5 basic GIS operations.(Chang, 2008) 1.Buffering 2.Overlay 3.Distance

Measurement 4.Pattern Analysis 5.Map Manipulations

GIS Analysis: Buffering Buffer are rings around features at a specified distance from the features.  Buffering creates two areas:

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area within a specified distance of selected features area beyond the selected features

Area within specified distance called “buffer zone” Feature of buffering may be points, lines or areas.

Buffer around points create circular buffer zones.

Buffer around lines creates a series of elongated buffer zones.

Buffer around areas creates buffer zone that extends outwards from the polygon boundaries.

Cont..

Buffering a Point e.g. All area within one mile of a city Buffering a Line e.g. All areas within 100 meters of a road Buffering an Area e.g. All areas within 500 meters of a wetlands area.

Cont..

Applications of Buffering

Government regulations may set 2 mile buffer zones along stream to minimize sedimentation from logging operations.  Environmental Department may restrict oil and gas well drilling within 500 feet of roads and highways.  Environmental Department may set a buffer zone of 30 m of factories from residential areas.  Transportation Department may declare a 5m buffers zone from main roads as a road reserves. 

GIS Analysis: Distance Measurement Distance measurements refers to measuring straight line (euclidean) distance between features.  Measurements can be made from points in a layer to points in another layer, or from each points in a layer to its nearest point or line in another layer.  A GIS package such as ArcGIS may include distance measurements as an analysis tool or as a joint operation between two table. 

GIS Analysis: Distance Measurement ď ľ

How far is it between two places? (measuring distances)

Cont.. ď ľ

Distance measurements can be used directly for data analysis

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Application: e.g use distance measures between home location and medical providers to evaluate geographic access to health services.

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Distance measures can also be used an input to data analysis.

Cont.. 

Many tasks require measurement from maps   

measurement of distance between two points measurement of perimeter. measurement of area, e.g. the area of a parcel of land

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Such measurements are tedious and inaccurate if made by hand.

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Measurement using GIS tools and digital databases is fast, reliable, and accurate.

GIS Analysis: Pattern Analysis Nearest neighbor analysis 

use the distance between each points and its closest neighboring point in a layer to determine if the point pattern is regular, random or clustered.

Spatial Autocorrelation 

nearest neighbor use only distances between points as input.

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spatial autocorrelation consider both point location and attribute at the location.

G-Statistic 

G statistic can separate clusters of high values from clusters of low values of data.

GIS Analysis: Pattern Analysis 

It deals with the examination and evaluation of spatial patterns and the processes of point features.

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Used to identify features that are closest to one another, calculate the distances around and between them.

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Monitor events in an area, find the area served by a facility, or find the features affected by an activity

Cont.. there are 3 general pattern:-

RANDOM

UNIFORM

CLUSTERED

GIS Analysis: Pattern Analysis Application of Pattern Analysis  for hot spot analysis and analyzing crime locations.  analyzing public health data, housing prices.  spatial autocorrelation useful for analyzing temporal changes to a spatial distribution, such as using Moran’s I for analyzing distribution of Latino population in Ada county.  spatial autocorrelation is important for validating the use of standard statistical test.

GIS Analysis: Point Pattern Analysis 

Pattern analysis refers to the use of quantitative methods for describing and analyzing the distribution pattern of spatial features.

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Pattern analysis can be reveal if a distribution pattern is random, dispersed or clustered.

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examples of pattern analysis:

Nearest neighbor analysis

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Spatial Auto Correlation (Moran’s I for measuring spatial auto correlation)

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Statistic for measuring high/low clustering

GIS Analysis: Map Manipulation   

Tools are available in GIS package for manipulation and managing maps in a database.

Like buffering and overlays, these tools are considered as basic GIS tools for analysis. basic map manipulation operation:•Eliminate •Update •Erase

•Dissolve •Clip •Append

•Split

•Select

Common Map Manipulation Operation Dissolves Aggregate features that have the same attributes values To simplify classified polygon layer Clip create new layer that iclude only those features of the input layer that fall within the area extent of the clip layer.

Appends pieces together two adjacent layer into single layer but does not remove the shared boundary between the layers Eliminate create new layer by removing features that meet user define query expression

Common Map Manipulation Operation Upadate replace the input layer with update layer and its features Erase removes from input layer those features that fall within area extent of the erase layer Split divide the input layer into two or more layer

GIS Analysis: Overlay 

An overlay operations combines the geometric and attributes of two feature layers to create the output.

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The geometry of the output represents the geometric intersection of features from the input layers.

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Features layers to be overlaid must be spatially registered on the same coordinates systems.

Spatial data overlay 

Spatial Overlay is analysis that allows you to extract data from one layer, such as block groups, to an overlay layer, such as a trade area. The analysis uses two layers: An input layer which provides the underlying data and an overlay layer which may contain additional information such as population or average household income.

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Spatial overlay analysis allows you to answer questions such as: 

How many households are in my overlay polygons?

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What are the demographic characteristics of each of my customers?

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What is the per capita income in this market area?

Overlay combines the geometries and attributes of two layers into a single layer.

Basic Overlay Operations Union Keeps all areas of two input layers in the output Intersect Preserves only the area common to the two input layers in the output Symmetrical Difference output Preserves areas common to only one of the input layers in the output Identity produced an output that has the same extent as the input layer.

Spatial Data Overlay 

Point in Polygon

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Line in polygon

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Polygon in Polygon

Point in Polygon 

The point in polygon operation is used to determine whether a point lies inside or outside a polygon.

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A spatial operation in which points from one feature dataset are overlaid on the polygons of another to determine which points are contained within the polygons.

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Occurs when point-like events must be compared to properties of the surrounding environment

Point in Polygon

Point in Polygon

Line in Polygon 

Polygon features of one input layer can be overlaid on lines (arcs) of another input layer.

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A line can be made up of many segments, Line-inPolygon analyses therefore identifies which polygon (if any) contains each line or line segment.

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The result of a Line-in-Polygon overlay is a new layer containing lines with additional attributes (ie. those attributes of the polygon within which the line falls).

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Sometimes a line segment falls directly on a polygon boundary instead of within the polygon. In this special case, the additional line attributes will contain the attributes of both polygons - lying to the left and right sides of the line.

Line in Polygon Which area contains the line segment?

Polygon in Polygon ď ľ

Polygon overlay is similar to the point-in-polygon operation in the sense that two sets of objects are involved

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From the discrete-object perspective, the task is to determine whether two area objects overlap, to determine the area of overlap, and to define the area formed by the overlap as one or more new area objects

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The continuous-field version of polygon overlay does this by first computing a new dataset in which the region is partitioned into smaller areas that have uniform characteristics on both variables.

Polygon in Polygon

where parcels (polygons) and flood zones (polygons) are overlayed to create a new polygon layer. The parcels are split where they are crossed by the flood zone boundary, and new polygons created.

The FID_flood value indicates whether polygons are outside ( -1) or inside the flood zone, and all polygons retain their original land use category values.

Applications of Overlay

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Investment company is looking for a land parcel that is zoned commercial, not subject to flooding, and not more than 1mile from heavy duty roads.

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Health department is mapping the area of cholera and want to warning the peoples not to stay in 30 m from the locations.

GIS Query      

Search or Browse the database.

Retrieve data.

Consist of two types: Attribute and Spatial Data Query.

Answer questions “How many?”

Answer questions “Where are they?”

Answer questions with more than one criteria using Boolean Operators (Logical) : AND, OR, NOT, XOR (exclusive OR) Relational (conditional) operators: =, >, <, <> (not equal to).

Attribute data query One of the selection methods you can use to select features in a layer is to select features using an attribute query. This is performed using the Select By Attributes tool

Attribute Data Query A request for records of features in a table based on their attribute values.

1.Logical expressions 2.Type of operation 3.Relational database query 4.SQL

Spatial data query Spatial queries require a filter geometry, such as a polygon, and a geometric relationship enumeration for a given feature layer. For example, return all the records for roads within the current map extent

SQL SQL (Structured Query Language) is a standard query language designed for relational databases.

The basic syntax of SQL, with the keywords in bold type, is select <attribute list> from <table> where <condition> The select keyword selects field(s) from a database, the from keyword selects table(s) from a database, and the where keyword specifies the condition or criteria for data query.

Simple SQL select Sale_date from Parcel where PIN = ‘P101’

More SQL select Parcel.Sale_date from Parcel, Owner where Parcel.PIN = Owner.PIN AND Owner_name = ‘Costello’

where Parcel.PIN = Owner.PIN AND Owner_name like ‘C%’ where Parcel.PIN = Owner.PIN AND Owner_name in (‘Wang’, ‘Smith’, ’Jones’)

Investment company is looking for a land parcel that is zoned as bare soil, not subject to flooding, within 500m from road and not more than 600m from river.